This invention relates to a method of eluting antimony ions from solid separation phases such as exchange resins and ligands covalently bonded to solid hydrophilic supports.
The removal and maintenance of antimony (Sb) levels at or below particular maximums in copper electrorefining electrolytes is essential in the copper refining industry throughout the world. Solid phases comprising chelating ion exchange resins and ligand containing solid hydrophilic separation phases have been developed which fairly selectively remove antimony from copper electrolye and other antimony containing source solutions by forming a complex or chelate between the antimony ion and the solid phase. Descriptions of the Sb separation operations of these materials using concentrated hydrochloric acid (6M HCl) elutions have been described in reports and articles such as Oda et al., Tamano Chelating Resin Adsorption Process, Metallurgical Review of MMIJ, Vol. 3, No. 2, (November 1986); Sasaki et al., Development of Antimony Removal Process for Copper Electrolyte, Hydrometallurgy and Electrometallurgy of Copper, Copper 91-Vol. III, page 245 (1991) and, et al., The Solvent Extraction and Ion Exchange Removal of As, Sb, and Bi from Copper Refining Electrolytes, Dept. of Metals and Materials Engineering, University of British Columbia, Vancouver B.C. (Jan. 20, 1992).
Ion exchange functionalites used to extract the Sb from source solutions typically are aminophosphonates (--N--PO.sub.2 H) but other functionalities such as [--N--(CH.sub.2 -COOH).sub.2 ] could also potentially be used. One class of suitable chelating ion exchange resins consist of a polystyrene support with aminophosphonate or other functional groups being used to bind the Sb ions. Representative of such ion exchange resins are the C-467 resin sold by Rohn & Haas and UR-3300 and MX-2 resins sold by Ubitika of Japan. Suitable chelating ligands attached to hydrophilic supports such as silica gel, titania, alumina, zirconia and the like consist of a ligand covalently attached to the solid support material. The ligand used can be macrocyclic or of linear or branched chain structure containing suitable functionalities to provide electrons for binding of antimony ions. Representative of such chelating ligands attached to solid hydrophilic supports are those manufactured by IBC Technologies, Inc. under the tradename SuperLig, e.g. Superlig 92.
Once the Sb ions are removed from solution and are complexed by the ion exchange resin or a ligand bonded to a solid phase, it becomes necessary to elute the Sb to regenerate the resin or ligand. A difficulty common to all of the solid separation phases presently being used is the requirement that an eluent must be an aqueous solution in which the antimony ions are either soluble or which has greater affinity for antimony than does the solid phase to which it has become attached thereby quantitatively stripping the antimony cations from the ion exchange resin or ligand without adversely affecting the solid phase. The solution currently found most effective is a concentrated hydrochloric acid (HCl) solution (i.e. typically about 6M HCl). The concentrated HCl elution requires that precautions be taken to insure that the HCl does not contact the electrolyte during operation. Also, the elution costs involved are of great importance. These include the costs of the HCl itself and the costs of either recycling the HCl via distillation and/or neutralizing the HCl for disposal. In either event the process is costly and counterproductive. For various reasons, it has long been desired to use a sulfuric acid (H.sub.2 SO.sub.4) solution for elution in place of the HCl. This should be advantageous in terms of both system chemical compatibility as well as an associated reduction in cost. This cost reduction would be particularly advantageous if the so-called "black acid" form of H.sub.2 SO.sub.4, which is readily available at copper refineries, could be used. H.sub.2 SO.sub.4 is not only less expensive than HCl, but economical disposal methods already exist within copper refineries for sulfuric acid disposal, particularly in the "black acid" form. Moreover, the use of H.sub.2 SO.sub.4 may also allow for the ability to recover antimony as a saleable product.
By "black acid" is meant an industrially produced form of sulfuric acid which also contains impurities such as As, Ni, Se as well as others. Some of the impurities give the acid a brownish to black hue. Hence, the name "black acid".
The major deterrent from using H.sub.2 SO.sub.4 as an eluent for antimony is the lack of solubility of antimony in sulfuric acid. Hence, the volume of sulfuric acid required for Sb elution is presently so large that it is prohibitive to its use. The solubility of antimony increases slightly as the temperature of H.sub.2 SO.sub.4 is raised. Furthermore, at too high elevated temperatures the stability of the ion exchange resins and, eventually, ligands bonded to hydrophilic solid supports may be affected.